Studies conducted in these laboratories are investigating pathways of aliphatic nitrogen oxidation by liver microsomes from different species. The results indicate that 2 distinct cytochrome P-450 dependent mechanisms are possible. One is a monoxygenase mechanism in which an amine is oxidized to a hydroxylamine. The second pathway involves a peroxidase-type mechanism whereby superoxide, generated by P-450 and NADPH, oxidizes a hydroxylamine or nitroso compound to the corresponding nitro compound. The structural requirements for these pathways are being examined.